Which parts of the image intensifier are typically curved?

The correct answer indicates that both the input phosphor and the photocathode of the image intensifier are typically curved. The input phosphor is shaped this way to optimize the collection of x-rays across a wide area, as it must capture the x-ray photons emitted from the patient. A curved input phosphor allows for a larger effective surface area for detection, which enhances image quality and reduces distortion.

The photocathode, which is directly attached to the input phosphor, is also curved to match the shape of the input phosphor and to ensure that it effectively converts the emitted light into photoelectrons. This curvature contributes to the efficient collection of light and the subsequent conversion process in the image intensifier.

The output phosphor, typically found at the end of the image intensifier, is usually flat, designed to allow for ease of coupling with the viewing system. Other components, like the channel electron multiplier, may have specific design characteristics, but they do not typically exhibit curvature like the input phosphor and photocathode.

This design choice for the input phosphor and photocathode is critical for maximizing image quality and overall function in fluoroscopic imaging systems.